Basically what you want to do is called bottom feeding. Lot's of big names do it, like nextag and pricegrabber. You might want to check out what they're bidding on by examining their websites.
The follow up question would be,
How do I monetize these five cent keywords?
Well, that's often referred to as arbitrage, where you buy low and sell high. So I guess that's what you want to do. With adsense I like to stay general then let the visitors channel themselves to their specifics.
Probably has to be more focused for aff.